The invention relates to an illumination device for a motor vehicle having a light source constructed of a number of semiconductor diodes which generate light in a first predetermined wavelength range, and a conversion layer on which a light beam generated from the light of the light source falls and by which the light beam is changed into a converted light beam, wherein the light of the light beam is converted into a second predetermined wave length range by a conversion material.
In order to generate light in a predetermined wavelength range, and in particular white light, with a motor vehicle illumination device, so-called conversion layers are used. The conversion layers include a suitable conversion material (such as for example phosphorus). For conversion of the light, a light beam generated by means of a light source is generally directed onto the conversion layer, so that a light beam is generated in a different wavelength range. In this case the problem exists that through scattering effects in the conversion layer a considerable widening of the light beam takes place, so that the definition of the light distribution generated with the illumination device is impaired.
The patent document WO 2010/058323 A1 describes an illumination device for a motor vehicle, in which the expansion of a color converted laser beam is delimited by use of a diaphragm on the conversion layer. In this case it is a disadvantage that the use of a diaphragm leads to a high loss of luminous flux (also called “luminous power”) which is often not acceptable in vehicle lighting technology.
Therefore, the object of the invention is to create an illumination device for a motor vehicle in which the light is color converted by use of a conversion layer and which nevertheless ensures a high definition of the generated light distribution.
This and other objects are achieved according to the invention by an illumination device comprising a light source constructed of a number of semiconductor diodes (i.e. at least one semiconductor diode), which generate light in a first predetermined wavelength range. The generated light is preferably monochromatic and is, for example, in the blue or violet wavelength range (i.e. 450 nm or 405 nm). Thus, the expression “wavelength range” should be interpreted broadly and may, for example, also relate to a fixed wavelength. The illumination device comprises a conversion layer onto which a light beam generated from the light of the light source falls and by which the light beam is changed into a converted light beam, wherein the light of the light beam is converted into a second predetermined wave length range by a conversion material of the conversion layer. In a particularly preferred embodiment, the conversion layer is configured in such a way that the light is converted into white light.
The illumination device according to the invention is designed such that from the converted light beam a predetermined light distribution is generated at a distance from the illumination device and, in particular, in the far field of the illumination device. The far field is understood to be the light distribution at a distance from the illumination device which is substantially greater than the dimensions of the illumination device and is located, in particular, in the region of 25 m and optionally more ahead of the illumination device. A light beam is understood to be a bundle of light beams which is limited in angle and in space, wherein the light beams in the bundle may be substantially parallel or may also diverge or converge. The light beam may be produced by the light source itself or optionally also by one or more further optical devices.
The illumination device according to the invention is characterized in that in at least a part-region of the surface of the conversion layer (i.e. seen in plan view of the conversion), a structure of one or more walls with a predetermined depth in the direction of the thickness of the conversion layer is provided. With this structure a suitable delimitation of the light distribution can be achieved directly by the conversion layer. As a result a light distribution with high definition can be generated in the region of the structure.
In a particularly preferred embodiment, the structure is a grid structure composed of grid walls with a predetermined depth in the direction of the thickness of the conversion layer, i.e. the structure comprises a plurality of walls in the form of grid walls. In this case the grid structure forms a plurality of surface segments adjoining one another which each contain conversion material and are delimited by grid walls. Depending upon the application, the surface segments can be completely or optionally only partially filled with conversion material. By the conversion layer with the grid structure contained therein, via the surface segments, a light beam falling on the conversion layer can be suitably delimited in its extent, so that by comparison with a conversion layer without a grid structure, sharply defined light distributions with high definition can be generated.
In a particularly preferred embodiment, the wall or walls of at least a part of the structure and, in particular, the grid walls of at least a part of the grid structure and preferably the entire grid structure, are reflective, so that the light scattered in the conversion layer is concentrated in the corresponding surface segment. Thus, in contrast to the diaphragm technology, no losses in the light intensity occur. Depending upon the application, the wall or walls can have diffusely reflecting or also mirroring characteristics. Nevertheless, the possibility also exists for the wall or walls of at least a part of the structure to be light-absorbing.
In a further preferred embodiment, the wall or walls of at least a part of the structure and, in particular, the grid walls of at least a part of the grid structure, are formed of metallic material or have a metallic coating. Likewise, the wall or walls can be made of plastic material with or without a metallic coating.
Depending upon the application, the individual surface segments can have different shapes. In preferred embodiments the surface segments, when seen in plan view of the conversion layer, are polygons, in particular rectangles, squares, triangles, rhombuses and/or hexagons. In this way a particularly high filling factor of the grid is achieved within the conversion layer.
The three-dimensional measurements of the surface segments in a plan view can vary depending upon the desired definition of the light distribution generated by the illumination device. The maximum extent of a respective surface segment in a plan view of the conversion layer is preferably between 5 μm and 500 μm.
The wall thickness of the grid walls of the grid structure is preferably chosen to be very small by comparison with the extent of the surface segments, in order thereby to avoid dark zones in the generated light distribution. In particular, the wall thickness of the grid walls is 20% or less of the maximum extent of the surface segments in a plan view of the conversion layer.
The depth of the wall or walls and, in particular, of the grid walls, can vary depending upon the embodiment and preferably corresponds to the thickness of the conversion layer, but may optionally also be less or more. Preferably, the depth of the wall or walls is between 50 μm and 500 μm.
In a further preferred configuration, a straight boundary line, which in the predetermined light distribution constitutes at least a portion of a light-dark boundary, is formed by grid walls of a plurality of surface segments of the grid structure which adjoin one another. For example a sharp light-dark boundary in a low beam light distribution can be formed by a horizontally extending straight boundary line and an adjoining obliquely extending boundary line, as is explained further in the detailed description with reference to FIG. 2.
In a particularly preferred embodiment, a laser light source is used as a light source in the illumination device according to the invention. This means that the semiconductor diodes comprise one or more laser diodes and, in particular, comprise exclusively laser diodes. In this way a light distribution with very high light intensity can be generated. The laser diodes preferably have a respective maximum output of at least 1 W and, in particular, between 1.5 and 5 W.
Compositions which are known per se can be used as materials for the conversion layer. In a particularly preferred embodiment the conversion layer is a phosphorus conversion layer, which in particular comprises nitride phosphorus, oxide nitride phosphorus or cerium-doped YAG phosphorus. These materials are used in particular for conversion of a blue or violet light beam into white light.
In a further particularly preferred embodiment a scanner is provided between the light source and conversion layer. In operation, the scanner changes the position of the light beam and in this way moves a light spot produced by the light beam for generation of the predetermined light distribution. The scanner may be configured as a conventional line scanner which moves the light beam and thus the light spot line by line at a fixed frequency. In this case the light source can be switched on or off or varied in intensity for production of the predetermined light distribution.
Instead of a line scanner, in the device according to the invention, a so-called vector scanner can also be used by which the scanning speed at which the light spot moves, and/or the scan path along which the light spot is moved, can be varied and can be controlled by a corresponding control unit for generating the predetermined light distribution. The scan path corresponds to the pattern of movement of the light spot which is produced by the change of position of the light beam. By means of a corresponding definition of a scan path it is possible to delimit the region in which a predetermined light distribution is present. Furthermore, by passing a number of times through the same regions according to the defined scan path, the light intensity in these regions can be correspondingly increased.
In a further preferred embodiment of the invention, the illumination device comprises an optical device in the form of an exit optical system, which in the direction of the beam path of the light beam is provided downstream of the conversion layer and reproduces the converted light beam corresponding to the predetermined light distribution. The optical device can be formed by one or more lenses and/or one or more reflectors.
Depending upon the application, the illumination device according to the invention may take on different functionalities. In one embodiment the illumination device comprises a headlight. A headlight is characterized in that it actively illuminates the surroundings of the vehicle. The illumination device according to the invention may optionally also comprise a signal lamp which is characterized in that it merely serves to give signals to other road users.
In a preferred variant the illumination device is configured as a headlight in such a way that in operation a low (dipped) beam characteristic is generated as the predetermined light distribution. Optionally, the illumination device may also be configured in such a way that in operation it generates a high beam characteristic as the predetermined light distribution.
In a further embodiment of the illumination device according to the invention, the conversion material and/or the thickness of the conversion layer differs in at least a part of the surface segments from other surface segments. In this way a light distribution of different colors or color temperatures can be generated.
The invention further relates to a conversion layer for use in the illumination device described above or one or more preferred variants of the illumination device described above. The illumination device is configured in such a way that a light beam falling on the conversion layer is converted from light in a first predetermined wavelength range into a converted light beam, wherein the light of the light beam is converted into a second predetermined wavelength range by way of a conversion material. The conversion layer is characterized in that in at least a part-region and, in particular, in the entire surface of the conversion layer, a structure composed of one or more walls with a predetermined depth in the direction of the thickness of the conversion layer is provided. This structure is preferably a grid structure composed of a plurality of grid walls with a predetermined depth in the direction of the thickness of the conversion layer, wherein the grid structure forms a plurality of surface segments adjoining one another which each contain conversion material and are delimited by grid walls.
In addition to the illumination device according to the invention, the invention further relates to a motor vehicle which comprises one or more of the illumination devices according to the invention.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawings.